Thermoregulation in Ectotherms Benny Cheong 3I305

Ectotherms Ectotherms are animals which regulate their body temperature via external means. These animals are reliant on the environment for the gain or loss of heat. As such, they need behavioral and structural adaptations for regulation of heat.

Adaptations to Warm Up As ectotherms need to gain heat from the environment, they display certain behaviour which allows them to warm up. – Basking in the Sun is the most commonly seen method, especially with the terrestrial reptiles, amphibians and arthropods, as the Sun is the main source of the Earth’s heat.

Marine Iguana The marine iguana inhabits only the Galapagos Islands, and it is the only lizard to have evolved to forage at sea. They occupy the barren rocks by the shore which are devoid of food, as such, they mainly feed on seaweed, found in the sea around them. Marine Iguanas in “Life in Cold Blood” by Attenborough:

Marine Iguana The Challenge: The sea around the Galapagos Islands remains cold all year round. Marine iguanas must thus gain enough body heat for them to survive the chilling temperatures of the sea (15-16 o C).

Marine Iguana The Solution: The marine iguana exploits the rocks they live on to increase their body temperature rapidly. – They gather at the uppermost rocks (which are the warmest) near the shore and bask in the sun for approximately half-an-hour before entering the seas to forage for seaweed.

Marine Iguana The Physics behind the solution: – The iguanas conduct heat through conduction and radiation. – Conduction: The iguanas conduct heat from the hot rocks. As heat is conducted more quickly through solids via lattice vibration, they are able to conduct heat rapidly. – Radiation: Heat energy from the Sun is transferred by EM waves to the iguana. Marine iguanas are also black, increasing heat absorbed via radiation as black surfaces are good absorbers of radiant energy.

Radiation Conduction Image Credits:

Namaqua Chameleon The Namaqua Chameleon lives in the extreme conditions of the desert. Living solitarily, they spend much time searching for mates. The Challenge: To heat up as quickly as possible in the morning, the only time of the day it is cool enough for them to be active. Namaqua Chameleon in “Life” by BBC

Namaqua Chameleon The Solution: The Namaqua Chameleon uses its colour changing abilities. – The side of the body facing the sun becomes darker-coloured. – The side of the body facing away from the sun becomes lighter-coloured.

Namaqua Chameleon Image Credits:

Namaqua Chameleon The Physics behind the solution: – Darker-coloured surfaces are good absorbers of radiant energy from the sun. – As such, making the side facing the sun darker- coloured increases the heat energy absorbed from the sun, allowing it to warm up quickly – Lighter-coloured surfaces are poor emitters of radiant energy. – As such, making the other side white decreases the heat energy lost from the chameleon by reducing the heat emitted.

Adaptations to Reduce Heat Since ectotherms have no control over how much heat they gain, they would overheat and perish if they gain too much thermal energy. Hence, they need adaptations to enable them to cool down/reduce heat gain.

Crocodile Crocodiles often lies near the river bank with its mouth wide open in the heat of the afternoon, remaining almost motionless. Image Credits:

Crocodile The Physics behind their behaviour: – The greater the exposed surface area, the more heat lost through radiation. – As such, by opening its mouth and increasing its exposed surface area, the crocodile increases the rate of heat loss. – Increase the rate of water vapour escaping from its body. – As water absorbs thermal energy from the crocodile when it changes into water vapour, the body temperature of the crocodile is reduced.

Sidewinder Snake Just like the Namaqua Chameleon, the Sidewinder also lives in the extremely hot desert. They are also active during parts of the day when temperatures are relatively low. The Challenge: To prevent themselves from overheating in the desert.

Sidewinder Snake The Solution: The sidewinder moves in a manner which obtained it its name- sidewinding, moving via side-to-side motions across the sand. Image Credits:

Sidewinder Snake The Physics behind The Solution: Recall the formula for the rate of conduction A in the formula represents the cross- sectional surface area between two objects.

Sidewinder Snake Image Credits: Parts of body coming into contact with sand circled in yellow- Only two parts of snake come into contact with sand at any point in time.

Sidewinder Snake The Physics behind The Solution: Through sidewinding, at any one point in time, only two small sections of the snake’s body comes into contact with the desert sand, reducing the cross-sectional surface area A. As such, Q/t is reduced greatly, preventing the sidewinder from conducting too much heat.

Credits BBC: Life in Cold Blood (2008) by David Attenborough BBC: Life (2009) Animal Planet *Information on this PowerPoint obtained by data from the videos coupled with application of Physics concepts learnt about Heat Transfer on Wikispaces.